Transcript The cytoplasmic membrane

Chair of Microbiology, Virology, and Immunology
Cell Structure of Bacteria.
Properties of prokaryotes and eukaryotes
Prokaryotes
Eukaryotes
The nucleoid has no membrane
separating it from the cytoplasm
Karyoplasm is separated from the
cytoplasm by membrane
Chromosome is a one ball of double Chromosome is more than one,
twisted DNA threads. Mitosis is There is a mitosis
absent
DNA of cytoplasm are represented DNA of cytoplasm are represented
in plasmids
in organelles
There aren’t cytoplasmic organelle There are cytoplasmic organelle
which is surrounded by membrane
which is surrounded by membrane
The respiratory system is localized The respiratory system is localized
in cytoplasmic membrane
mitochondrion
There are
cytoplasm
ribosome
70S
in There are ribosome 80S
cytoplasm
in
Peptidoglycan are included in cell’s Peptidoglycan aren’t included in
wall (Murein)
cell’s wall
The structure of procaryotes
Nucleus. The prokaryotic nucleus can
be seen with the light microscope in
stained material. It is Feulgenpositive, indicating the presence of
DNA. Histonelike proteins have
recently been discovered in bacteria
and presumably play a role similar to
that of histones in eukaryotic
chromatin
The DNA is seen to be a single,
continuous,
"giant"
circular
molecule with a molecular weight of
approximately 3 X 109. The
unfolded nuclear DNA would be
about 1-3 mm long (compared with
an average length of 1 to 2 µm for
bacterial cells)
Plasmids
 small circular, double-stranded DNA
 free or integrated into the chromosome
 duplicated and passed on to offspring
 not essential to bacterial growth & metabolism
 may encode antibiotic resistance, tolerance to toxic metals,
enzymes & toxins
 used in genetic engineering- readily manipulated & transferred from
cell to cell
 There may be several different plasmids in one cell and the
numbers of each may vary from only one to 100s in a cell
Plasmids:
R, Col, Hly, Ent, Sal
Prokaryotic Ribosome
 A ribosome (70 S) is a
combination of RNA and
protein, and is the site for
protein synthesis
 Composed of large (50S)
and small (30S) subunits
 S = Svedverg unit,
measures molecular size
The 80S ribosomes of
eukaryotes are made up of
40S and 60S subunits.
Inclusions, granules
• Storage granules
– Metachromatic
granules
– Polysaccharide
granules
– Lipid inclusions
– Sulfur granules
– Carboxyzomes
– Magnetosomes
• Gas vesicles
Volutin granules
Corynebacterium diphtheriae
Neisser's staining
Loeffler's technique
Cell Envelope
Composted of
A. The cytoplasmic
membrane
To act as a physical
barrier btw cytoplasm and
environments and
selectively controls the
movement of substaces
into and out of the cell
“Semipermeable”
B. Cell wall
The rigid layer that
protect the fragile
cytoplasmic membrane
from rupturing
To maintains cell’s shape
C. Capsule or slime
layer (glycocalyx)
Cell membrane
Bacterial plasma membrane are
composed of 40 percent
phospholipid and 60 percent
protein.
The phospholipids are amphoteric
molecules with a polar hydrophilic
glycerol "head" attached via an
ester bond to two nonpolar
hydrophobic fatty acid tails, which
naturally form a bilayer in aqueous
environments. Dispersed within the
bilayer are various structural and
enzymatic proteins which carry out
most membrane functions.
Peripheral
Membrane
Protein
Phospholipid
Integral
Membrane
Protein
Peripheral
Membrane
Protein
Mesosome
The predominant functions of bacterial membranes are:
1. Osmotic or permeability barrier;
2. Location of transport systems for specific solutes (nutrients and ions);
3. Energy generating functions, involving respiratory and photosynthetic
electron transport systems, establishment of proton motive force, and
transmembranous, ATP-synthesizing ATPase;
4. Synthesis of membrane lipids (including lipopolysaccharide in Gramnegative cells);
5. Synthesis of murein (cell wall peptidoglycan);
6. Assembly and secretion of extracytoplasmic proteins;
7. Coordination of DNA replication and segregation with septum formation
and cell division;
8. Chemotaxis (both motility per se and sensing functions);
9. Location of specialized enzyme system.
Cell wall
• Unique chemical structure
– Distinguishes Gram positive from Gram-negative
– bacteria and archaea bacterial species
• Rigidity of cell wall is due to peptidoglycan
(PTG)
– Compound found only in bacteria
– Archaea –psudomurein or other sugars, proteins,
glycoproteins
• Many antimicrobial interfere with synthesis of
PTG
• Penicillin; Lysozyme
Structure of peptidoglycan
•
Basic structure of peptidoglycan
– Alternating series of two
subunits
• N-acetylglucosamin (NAG)
• N-acetylmuramic acid (NAM)
– Joined subunits form glycan
chain
• Glycan chains held together
by string of four amino acids
– Tetrapeptide chain:
L-ala-D-glu-DAP-D-ala
L-ala-D-glu-Lys-D-ala
•
Interpeptide bridge
Differences of cell wall structure in Grampositive and Gram negative cells
Structures associated with gram-positive and gram-negative cell walls.
L Forms
Glycocalyx
 Capsule
Protects bacteria from phagocytic cells
 Slime layer
Enable attachment and aggregation of
bacterial cells
Capsules
Most prokaryotes contain some sort of a
polysaccharide layer outside of the cell wall polymer
Only capsule of B. anthracis consist of polypeptide
(polyglutamic acid)
Capsule
The capsule is covalently
bound to the cell wall.
Associated with virulence in
bacteria.
Example:
Streptococcus pneumoniae
Slime Layer
The slime layer is
loosely bound to the
cell.
Carbohydrate rich
material enhances
adherence of cells on
surfaces
Example:
Streptococcus mutans
and “plaque formation”
Biofilms
The slime layer is
associated with cell
aggregation and the
formation of biofilms
Example:
Staphylococcus
epidermidis biofilms
on catheter tips
General capsule function
•Adhesion
•Avoidance of immune response
•Protection from dehydration
•Protection of bacterial cells from engulfment
by protozoa or white blood cells (phagocytes), or
from attack by antimicrobial agents of plant or
animal origin.
•They provide virulent properties of bacteria
(S. pneumoniae, B. anthracis)
Flagella
• 3 parts
– filament – long, thin,
helical structure
composed of proteins
– hook- curved sheath
– basal body – stack of
rings firmly anchored
in cell wall
• rotates 360o
• 1-2 or many
distributed over entire
cell
• functions in motility
Flagellar arrangements
1. Monotrichous – single flagellum at
one end (cholera vibrio, blue pus
bacillus),
2. Lophotrichous – small bunches
arising from one end of cell (bluegreen milk bacillus,
Alcaligenes faecalis)
3. Amphitrichous – flagella at both
ends of cell (Spirillum volutans),
4. Peritrichous – flagella dispersed
over surface of cell, slowest E.
coli, salmonellae of enteric fever
and paratyphoids A and B
Bacterial Motility
Flagella are
important for:
Motility
(dispersal)
Antigenic
determinant
Number and
location species
specific
The rotation of the flagella
enables bacteria to be motile.
Pili and Fimbriae
• Short, hair-like structures on the surfaces of procaryotic cells
• Proteinaceuse filaments (~20 nm in diameter)
• Very common in Gram-negative bacteria
• Functions:
– Adherence to surface/ substrates: teeth, tissues
– Involved in transfer of genetic information btw cells
– Have nothing to do with bacterial movement (Except the twitching
movement of Pseudomonas)
Fimbriae are smaller than flagella and are important for attachment
Bacterial endospores
• Bacterial spores are often called “endospore” (since they are
formed within the vegetative cell)
• Produced in response to nutrient limitation or extreme
environments
• Highly resistant
• Highly dehydrated (15% water)
• Metabolically inactive
• Stable for years
• Not reproductive
• Functions: to survive under an extreme growth conditions such
as high temperature, drought, etc.
Bacillus, Clostridium, Sporolactobacillus, Thermoactinomyces,
Sporosarcina, Desulfotomaculum species sporulate
Spore
Spores
• Key compositions:
– Dipicolinic acid (DPA)
– Calcium (Ca2+)
• Structure
–
–
–
–
–
–
Core / Cytoplasm
Plasma membrane
Core wall/ spore wall
Cortex
Spore coat
Exosporium
Endospores
The sporulation process begins when nutritional conditions become
unfavorable, depletion of the nitrogen or carbon source (or both) being the most
significant factor. Sporulation involves the production of many new structures,
enzymes, and metabolites along with the disappearance of many vegetative
cell components.
Spores are located:
1) Centrally (B. anthracis);
2) Terminally (С. tetani);
3) Subterminally (C. botulinum, C. perfringens)
The spores of certain bacilli are capable of
withstanding
boiling
and
high
concentrations of disinfectants. They are
killed in an autoclave exposed to saturated
steam, at a temperature of 115-125 C, and
also at a temperature of 150-170 C in a
Pasteur hot-air oven.
Important Point: